We like the BZZZzzzzz when phone in silent mode (enable vibration). You can do that on anything now :) That's the little buzzing motor, and for any haptic feedback project you'll want to pick up a few of them. These motors are tiny discs, completely sealed up so they're easy to use and embed.
Two wires are used to control/power the vibe. Simply provide power from a battery or microcontroller pin (red is positive, blue is negative) and it will vibrate and produce the buzz sound. Works from 2V up to 5V, higher voltages result in more current draw but also a stronger vibration.
If you want to reduce the current draw/strength (for example, to control it directly from an Arduino pin) try putting a resistor (100 to 1000 ohms) in series. For full power control, a small NPN transistor (2222) can control a motor easily, some experimentation may be required!
